The stator coil of a conventional electrical motor typically comprises long straight sections joined by curved end windings. The coil is usually mounted to the motor by mechanically pressing the straight sections into slots. The coil is then held in place by an interference fit or by slot closure devices. The coil may be vacuum pressure impregnated.
In use, differential thermal expansion occurs between the coil and the coil mount, but the end windings of the coil confer some flexibility that allows a degree of movement between straight sections of the coil and the slots. This movement is usually sufficient to accommodate the differential thermal expansion.
Conventional coils also have semi-conductive wraps to achieve the necessary earthing. The slots are typically the means by which electrically conductive earthing paths for the wrap are provided.
However, in several applications there is a demand for accurately manufactured stator coils which have high mechanical and electrical integrity. This demand exists, for example, in transverse flux motors (TFMs), which are permanent magnet machines under development for ship propulsion.
In contrast to the geometrically complex electrical stator coil of conventional motors, a TFM has a simple solenoidal (i.e. substantially circular) coil. Although this shape is geometrically simple, its manufacture and operation at high voltages require advanced manufacturing and installation techniques.
For example, the operation of TFM stator coils at high voltages and high switching rates, such as those encountered when using inverter based drives, places significant demands on the motor. In particular, it has been found difficult to adapt the conventional method of mounting the coil to the motor such that the differential thermal expansions experienced in use are accommodated while simultaneously the requirements for controlled electrical grounding of the coil's semi-conductor wrap and conductive heat removal are met.
The problem is exacerbated by the limited space available for the coil and coil mounting in the overall TFM.